Comparing from: 7.0.11
Comparing to: 7.0.13
Screenshot:

I've noticed this as well. It hasn't affected my experience at all, but you're not the only one seeing this.

Can confirm this is still a problem in 7.0.17

maybe this is why ?

http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/1289765-waila-1-5-7-for-1-7-10-1-6-0-for-1-8-1?comment=948